1. Field of the Invention
This invention relates to an illuminating device in an ophthalmometer which is a measuring device for measuring the curvature radius of the cornea of an eye, the astigmatism of the cornea, etc.
2. Description of the Prior Art
There are various types of the ophthalmometer. By the operating method involved during measurement, they may generally be classified into the Javal-Schiotz type wherein measurement is effected by moving a chart projected upon the cornea or the like and the Sutcliffe or the Littmann type wherein measurement is effected by operating an optical member within a viewing optical system.
The present invention pertains to the ophthalmometer of the latter type and the conventional ophthalmometer of such type will hereinafter be described with respect, for example, to the Sutcliffe type ophthalmometer.
Referring to FIG. 1 of the accompanying drawings, there is shown the Sutcliffe type ophthalmometer according to the prior art. A chart image projected upon the cornea of an eye 1 to be examined may be provided by an illuminating light passed from a light source 2 disposed laterally of a viewing optical system and directed through a diffuser plate 3 and via a mirror 4 obliquely disposed on the optical axis T, to illuminate a chart plate 5. The chart image projected upon the cornea of the eye 1 to be examined may be viewed by the viewing optical system comprising an objective 6 and an eye-piece 7, through light-transmitting portions formed centrally of the chart plate 5 and of the mirror 4.
As the chart image is being so viewed, the curvature radius of the cornea of the eye 1 may be measured by operating an optical measurement adjust member 8 (which comprises two prisms for measuring two principal radial lines of the cornea astigmatism, respectively, the prisms being movable along the optical axis T to measure the curvature radius or like factor of the cornea).
In the conventional ophthalmometer of the described type, however, the light source means for illuminating the chart is projectedly disposed laterally outwardly of the viewing optical system and the mirror for directing the light from the source to the chart is obliquely disposed between the objective and the chart plate, and this has led to a larger size of the entire device which is particularly undesirable as an ophthalmometer wherein various operations occur with the viewing optical system being looked into.